1. Field of the Invention
This invention relates to data backups systems. Particularly, this invention relates to restoring data backups with hardware and software backup and restore processes such that consistency of disk signatures is maintained before and after restore.
2. Description of the Related Art
In a typical computer operating system, such as the Windows Operating System, every physical disk detected by the operating system is assigned a unique disk signature when the disk is first initialized. In particular, the drive letter and mount point assignments are keyed off the disk signature. Data backups, such as snapshot backups, are created and restored within this hardware.
At a high level, two kinds of snapshot technologies can be defined, hardware-based and software-based. Typically, a hardware-based snapshot may be created by the firmware embedded in the hardware. However, it is important to note that such backups may be requested by software (e.g., as the IBM Tivoli Storage Manager (TSM) for copy services product does). On the other hand, software-based snapshots may be created by the software, typically either by a file system or a logical volume manager. After a hardware-based snapshot restore, such as an “instant restore” in the TSM product family, of a Logical Unit Number (LUN) from a LUN created using a copy service, such as Volume Shadow Copy Services (VSS) snapshot, the operating system does not reassign driver letters and mount points that were originally assigned to the source disk. This, in turn, causes data access problems for the applications that store and access data on the volume after an instant restore. This problem is apparent after the system reboots, when the device scan and initialization takes place, but can also occur without a reboot. The cause of the problem is that the operating system identifies the source disk as a new LUN after the instant restore and assigns a new disk signature to the source LUN, while the old driver letter remains assigned to the disk signature prior to the restore.
VSS is a Microsoft platform that operates to assist driving both hardware-based as well as software-based snapshots from a single interface. The described inconsistency may be specific to the snapshot backups created using a software copy service that uses underlying VSS and does not exist if the snapshot is created outside of the VSS, for example using the user interface offered by the hardware vendor. It should be noted that VSS alone does not create a snapshot; an underlying snapshot service is also required.
However, the described problem occurs for the snapshots created using VSS (i.e., that are software-driven) because the VSS model requires snapshot to be made available (with an exception) to the Windows host system, known as import in VSS terminology. Backups performed by such software access both source and target LUNs at the same time, that are likely from the same host. In order to support simultaneous access, the software import process updates the disk signature on the snapshot backup LUN without user awareness. In short, a target LUN in hardware-driven snapshot is not identical to its source LUN and differs in disk signature. Some systems and techniques have been developed for managing data backups, particularly snapshot data backups.
U.S. Patent Application Publication No. 2003/0204597 by Arakawa et al., published Oct. 30, 2003, discloses a storage system configured to provide a storage area to a host coupled to the storage system. This includes a first storage device of first type being configured to store data and provide one or more data-storage-related functions. A second storage device of second type is configured to store data and provide one or more data-storage-related functions. A virtual volume provides a storage location and being associated with at least one of the first and second storage devices. A database includes information relating to the one or more data-storage-related functions that the first and second storage devices are configured to perform. A first server is coupled to the first and second storage devices and having access to the database, the first server being configured to access the database in response to a data-storage-related-function request from the host involving at least one of the first and second storage devices. The database is accessed to determine whether or not the at least one of the first and second storage devices is capable of performing the request from the host. The first server further being configured to perform the request if the determination is negative or provide an instruction to the at least one of the first and second storage devices to perform to the request if the determination is positive.
U.S. Patent Application Publication No. 2005/0240635 by Kapoor et al., published Oct. 27, 2005, discloses methods and systems of snapshot management of a file system in a data storage system. To represent the snapshots, the invention maintains pointers to the root block pointer of each snapshot. When the active file system is modified, this invention avoids overwriting any blocks used by previous snapshots by allocating new blocks for the modified blocks. When the invention needs to put an established block in a new location, it must update a parent block to point to the new location. The update to the parent block may then require allocating a new block for the new parent block and so forth. Parts of the file system not modified since a snapshot remain in place. The amount of space required to represent snapshots scales with the fraction of the file system that users modify. To maintain snapshot integrity, this invention keeps track of the first and last snapshots that use each block in space map blocks spread throughout the file system data space. When users delete snapshots, this invention may use a background process to find blocks no longer used by any snapshot and makes them available for future use.
U.S. Patent Application Publication No. 2005/0004979 by Berkowitz et al., published Jan. 6, 2005, discloses a system and method of transporting volumes of information from one host computer system to another using point-in-time copies of LUNs but wherein the hardware provider does not necessarily understand the volume configuration of the data. The system and method involves an intermediate layer, i.e., a point-in-time copy interface layer that communicates with both a requesting host computer system and a hardware provider to enable the transfer of volumes of information without requiring that the hardware provider understand the volume information.
U.S. Patent Application Publication No. 2005/0108292 by Burton et al., published May 19, 2005, discloses an apparatus for managing incremental storage, including a storage pool management module that allocates storage volumes to a virtual volume. Also included is an incremental log corresponding to the virtual volume, which maps virtual addresses to storage addresses. The apparatus may also include a replication module that sends replicated data to the virtual volume and a policy management module that determines allocation criteria for the storage pool management module. In one embodiment, the incremental log includes a lookup table that translates read and write requests to physical addresses on storage volumes within the virtual volume. The replicated data may include incremental snapshot data corresponding to one or more primary volumes. The various embodiments of the virtual incremental storage apparatus, method, and system facilitate dynamic adjustment of the storage capacity of the virtual volume to accommodate changing amounts of storage utilization.
Existing systems and methods do not address the problem of inconsistent LUNs in a snapshot backup and restore, e.g. arising between a software snapshot and a hardware restore described above. Thus, there is a need in the art for systems and methods to ensure consistency of disk signatures before and after a hardware-based snapshot restore from a LUN created by a software-based snapshot. These and other needs are met by the present invention as detailed hereafter.